Supplementary information
On the pH Dependence of the Potential of Maximum Entropy of
Ir(111) Electrodes
Alberto Ganassin 1, Paula Sebastián 2, Víctor Climent 2, Wolfgang Schuhmann 1,
Aliaksandr S. Bandarenka 3,*, Juan Feliu 2,*
1 Analytical Chemistry - Center for Electrochemical Sciences (CES); Ruhr-Universität Bochum,
Universitätsstr. 150, 44780 Bochum, Germany
2 Instituto de Electroquímica, Universidad de Alicante, Apartado 99,
E-03080 Alicante, España-Spain
3 Energy Conversion and Storage – ECS, Physik-Department, Technische Universität München,
James-Franck-Straße 1, 85748 Garching, Germany
*Corresponding authors, e-mails:
[email protected], tel. +49 (0) 89 289 12531 (A.S. Bandarenka)
[email protected] , tel. +34 965 909 301 (J. Feliu)
pH1
2
pH2
E / mV
0
-2
pH3
-4
-6
150mV vs RHE
-8
0
1
2
3
4
5
t / s
Figure S1: Laser induced potential transients of Pt(111) recorded at 150 mV vs RHE in Arsaturated solution of:.0.1 M HClO4 (black line, pH=1), 0.01 M HClO4 + 0.099 M KClO4 (red line,
pH=2) and 1 mM HClO4 + 0.1 M KClO4 (purple line, pH=3).
Determination of the thermal coefficients (dE/dT)q from the laser induced E-t transients:
1 ∂EM
t
∆E= 2 ( ∂T ) T0 √t
q
0
(1)
Where EM is the electrode potential, T0 is the temperature, t is the time, and q is the electrode
charge. From the Electrocapillary equation it can be shown that (dEM/dT)q is equivalent to
(dS/dq)T in the absence of specific adsorption, where S is the entropy of formation of the
double layer [1,2]. The thermal coefficient is extracted from the laser induced potential transient
data by the following graphic procedure. If the reorganization of the double layer is fast enough
in the time scale employed, and the change in the temperature is small, then the potential change
E should vary linearly with the square root of time, according to equation (1). Therefore, the
thermal coefficient can be extracted from the slope of these plots:
∂EM 2*slope
=
(mV K-1 )
∂T ΔT0 √t0
(2)
The maximum temperature change T0 can be calculated from the optical properties of the
surface and the thermal properties of the adjacent phases. For Ir(111) the maximum temperature
change reached is 25ºC for a laser beam energy of 1 mJ.
Figure S2: Dependencies of the electrode potential on the inverse of the square root of the time
of the transients recorded at pH=1 and pH=3 in perchloric solutions whose composition is as
described in the manuscript (Figure 1).
Figure S3: The results of the CO displacement experiment on Ir (111) in 0.1 M HClO4 at 0.3 V
vs. RHE. Negatively charged species are displaced from the surface at potentials more positive
than the anodic peak at ~0.25V vs RHE observed in cyclic voltammetry in Figure 2 of the
manuscript.
Figure S4: The results of the CO displacement experiment using Ir (111) electrodes in contact
with 0.1 M HClO4 at 0.15 V vs. RHE. Positively charged species are displaced from the surface
at potentials more negative than the anodic peak at ~0.25 V vs RHE as observed in the
voltammograms shown in Figure 2 of the manuscript.
Figure S5: Typical CO stripping voltammogram obtained for Ir(111) in 10 mM HClO4 + 0.09 M
KClO4 (pH=2) electrolytes at 0.3 V vs RHE. Red line represents the CO stripping and the black
line shows the cathodic scan after the stripping. Scan rate 20 mV/s.
Figure S6: Typical CO stripping voltammogram obtained in 1 mM HClO4 + 0.1 M KClO4
(pH=3) for Ir(111) electrodes after the CO displacement at 0.3 V vs RHE. Red line represents the
CO stripping and the black line shows the cathodic scan after the stripping. Scan rate 20 mV/s.
Figure S7: CO stripping in 0.08 M KClO4 + 0.02 M NaF/HF (pH=4) after the CO displacement
at 0.3 V vs RHE. Red line represents the CO stripping and the black line the cathodic scan after
stripping. Scan rate 20 mV/s.
References
[1] N. Garcia-Araez, V. Climent, J. M. Feliu, in Modern aspects of electrochemistry, Vol. 51
(Ed: C. G. Vayenas), Springer, New York 2011, pp. 1–103.
[2] V.A. Benderskii, G.I. Velichko, J. Electroanal. Chem. Interfacial Electrochem. 1982, 140, 1.